1. Field of the Invention
This invention relates to an acoustic baffle for an automobile cavity. In one of its aspects, the invention relates to a composite integral baffle which includes a heat expandable sealing material and rigid support of predetermined shape that can be mounted in a cavity such as a hollow pillar of an automobile or similar vehicle. In another of its aspects, the invention relates to a method for manufacturing the composite integral baffle that includes a heat expandable sealing material and rigid support of predetermined shape.
2. Description of the Related Art
With increased focus on interior "noise quality" for automobiles, many new and existing material applications are being investigated. One existing application is the use of heat reactive, expanding sealing materials used in the vehicle body structures known as pillars. One particular problem to the acoustical engineer is the nuisance noise the "pillars", or hollow channels in the vehicle body structures, transmit to the passenger compartment. The pillars are linked together to define the body structure from front to back of the automobile. Blocking these channels and the noise path has proven to help a vehicle's perceived sound quality.
The nuisance noise that occurs in these pillars is related to power train, wind, tire, and road noise. Over the years, various solutions have been used to minimize the energy level of noise that flows from these sources to these pillars. A current approach is to block the path of noise with heat reactive, expandable sealing materials mounted to support plates to create a "baffle". Baffles are strategically located within the body structure in a pattern that helps to eliminate propagation of noise into the vehicle passenger compartment.
The varying vehicle body styles in the automotive industry has lead to the development of numerous baffle constructions, particularly since pillar definition is becoming more complex. This complexity has required designs to become more precise, yet flexible for easy installation. Further, because sealing effectiveness of any baffle design is critical to acoustic performance, the presence of any holes in the sealed out perimeter of the baffle within the channel drastically reduces the acoustic response.
Many attempts have been made to seal these cavities, including spraying of a sealant into the cavity, introducing foreign products into the cavity, and using fiberglass matting and the like. These past efforts have not been entirely satisfactory because of the inefficiency of the sealing and baffling methods, the relatively high cost of the sealing process, and the fact that erratic sealing has resulted in many instances.
Foaming in place has not been totally satisfactory because of the difficulty in controlling where the foam travels upon introduction of the foam into a vehicle body cavity, and the fact that more foam than is actually needed is usually introduced into the body cavity to provide some degree of redundancy in preventing the passage of moisture into and the blockage of noise within the cavity during use of the vehicle. Furthermore, foams have a finite life insofar as they become rigid with time, thus limiting the time period available in which the foam may be introduced in the vehicle cavity. In addition, if the interior surface of the cavity has a somewhat oily surface, the foams would not adequately adhere to that surface, thereby resulting in an ineffective seal.
It is also known to use an expandable baffle for sealing the cavity of an automobile pillar with a sheet of heat expandable sealing material mounted on a rigid plastic or metal support that is formed in the shape corresponding to the shape of the cross-section of the cavity to be sealed. The heat expandable material has been mounted to a single support sheet of has been sandwiched between two rigid support sheets. The composite material is mounted inside the cavity and the sealing material is expanded when the automobile is subjected to a high temperature, often during the paint baking cycle, at which point the sealing material expands to seal the cavity at the cross-section. This method generally produces a superior acoustic seal, but the manufacture of the combined heat activated sealing material and support plate is costly. In the case of the use of a single support sheet, the heat expandable material tends to form a dome shape while the sealing occurs only at the edges of the dome. Much heat expandable material is wasted. In the case of the use of a sandwich construction, the expansion tends to be directional but there is significant excess material between the two support sheets. Thus, there is much wasted sealing material. Furthermore, depending upon the dimensions of the cross-section or space restrictions for mounting the expandable material and support plate, it may not be possible to seal a pillar cavity at the preferred point. That is, the direction of expansion cannot be controlled.